1. Technical Field
Various embodiments of the present disclosure generally relate to photo masks used in fabrication of semiconductor devices, and to reflection type blank masks, methods of fabricating the same, and methods of fabricating reflection type photo masks using the same.
2. Related Art
As semiconductor devices become more highly integrated, sizes of circuit patterns constituting the semiconductor devices have been continuously reduced. Thus, there may be some limitations in realizing the fine patterns with a photolithography process utilizing ultraviolet (UV) rays. Accordingly, an extreme ultraviolet (EUV) lithography process has been proposed to form the fine patterns of the semiconductor devices. The EUV rays may have relatively short wavelengths. For example, the EUV rays may have a wave length of about 0.2 nanometers to about 100 nanometers.
A reflection type mask may be used in the EUV lithography process. The reflection type mask may include a laminated reflection layer formed on a transparent substrate and absorption layer patterns (e.g., metal patterns) formed on the laminated reflection layer. The laminated reflection layer exposed by absorption layer patterns may reflects the EUV rays and the absorption layer patterns may absorbs the EUV rays. Planar images of the absorption layer patterns (or planar images of the exposed portions of the reflection layer) may be transferred on a wafer using a EUV lithography apparatus (e.g., an exposure apparatus) with the reflection type mask. During the EUV lithography process, the EUV rays may be irradiated on the reflection type mask. The absorption layer patterns may absorb the EUV rays while the EUV lithography process is performed. In contrast, the EUV rays irradiated onto the exposed portions of the laminated reflection layer may be reflected toward a resist layer coated on the wafer through a mirror optical system.
There are many issues in the development of the EUV lithography process. For example, the EUV lithography process may be affected by substrate defects of the reflection type masks used in the EUV lithography process. In particular, it may be difficult to fabricate blank masks without any defects because the laminated reflection layer of the EUV mask is formed by stacking a plurality of layers, for example, about eighty layers of molybdenum/silicon. In order to minimize the influence of the substrate defects (e.g., blank defects) on the lithography process, the coordinates and sizes of the blank defects should be accurately recognized.
Fiducial marks may be formed in the transparent substrate to increase the accuracy of the substrate defect inspection, and the fiducial marks may be used as reference position marks during inspection of the substrate defects. The fiducial marks may be formed by etching the mask substrate before the laminated reflection layer is formed. Thus, the fiducial marks may be formed to have a recessed shape. Meanwhile, the fiducial marks may be formed by coating a resist layer on the mask substrate, exposing the resist layer, developing the exposed resist layer, etching the mask substrate using the developed resist layer as an etch mask, removing the developed resist layer, and cleaning the etched mask substrate. Accordingly, additional substrate defects may be formed while the fiducial marks are formed. These substrate defects may be transferred on the wafer even through laminated reflection layer is formed on the mask substrate having the substrate defects. That is, the substrate defects may degrade the quality of the reflection type masks.